$ A = \left[\begin{array}{rrr}2 & 0 & 2 \\ 1 & 2 & 0 \\ 2 & 1 & 0\end{array}\right]$ What is $ A^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}0 & -\frac{1}{3} & \frac{2}{3} \\ 0 & \frac{2}{3} & -\frac{1}{3} \\ \frac{1}{2} & \frac{1}{3} & -\frac{2}{3}\end{array}\right]$